This project is the pilot step necessary to develop a system of vaccination pharmacoepidemiology that associates a sophisticated analytical approach, appropriate for this challenge and case series analysis, with the use of linked medicoadministrative data for hospitalisations the reimbursement of healthcare costs. This linkage of medicoadministrative data is new in France. The example of the risk of hospitalisation for febrile convulsions in infants less than two years old following vaccination against diphtheria, tetanus and pertussis is given as the reference association. This choice is justified by the numerous publications over many years on the existence of this association (Miller et al BMJ 1981, Farrington et al Lancet 1995). In addition, as case series analyses have been carried out to assess this risk, the results can be compared directly (Lancet 1995). The study to determine whether the analysis tools are suitable for the data will be tackled at the following levels: